Bohemia don't always seem the most organised with how they update their games, whether it's DayZ or Take On Mars, but they have been much better over the past few years with Arma 3 [official site]. I like especially their regular posts about their internal development roadmap, and there's now a post and new footage outlining updates and expansions to come in 2016.
There are three distinct but connected items on the list.
The first is the Nexus Update, which focuses on "improvement of core features and multiplayer systems." This includes a web-based service for the community to use to team up together, and new content for the End Game mode which tries to shape Arma's many systems into a cooperative, more easily explained experience.
The second is the Eden update, which will introduce a "3D scenario editor" as well as a new server browser and "several usability tweaks" to the games controls and interface. There's a video of the Eden Editor embedded in this post, showing the kinds of things you can build with it.
Both of those updates should come around the end of this year, before 2016 sees the release of the next major expansion, called Arma 3 Apex. It will bring a co-op campaign, a new landmass called Tanoa, as well as new vehicles, weapons, vehicle classes, and a slew of more usability improvements. There's a video showing the new landmass below, which looks more like the kind of place you'd go on holiday than most Arma settings.